PT  - JOURNAL ARTICLE
AU  - Salaheddin M. Mahmud
AU  - Marissa Becker
AU  - Yoav Keynan
AU  - Lawrence Elliott
AU  - Laura H. Thompson
AU  - Keith Fowke
AU  - Lisa Avery
AU  - Paul Van Caeseele
AU  - Sande Harlos
AU  - James Blanchard
AU  - Magdy Dawood
TI  - Estimated cumulative incidence of pandemic (H1N1) influenza among pregnant women during the first wave of the 2009 pandemic
AID  - 10.1503/cmaj.100488
DP  - 2010 Oct 05
TA  - Canadian Medical Association Journal
PG  - 1522--1524
VI  - 182
IP  - 14
4099  - http://www.cmaj.ca/content/182/14/1522.short
4100  - http://www.cmaj.ca/content/182/14/1522.full
SO  - CMAJ2010 Oct 05; 182
AB  - Background: Hospitalization and lab confirmed cases of H1N1 have been reported during the first wave of the 2009 pandemic but these are not accurate measures of influenza incidence in the population. We estimated the cumulative incidence of pandemic (H1N1) influenza among pregnant women in the province of Manitoba during the first wave of the 2009 pandemic. Methods: Two panels of stored frozen serum specimens collected for routine prenatal screening were randomly selected for testing before (March 2009, n = 252) and after (August 2009, n = 296) the first wave of the pandemic. A standard hemagglutination inhibition assay was used to detect the presence of IgG antibodies against the pandemic (H1N1) 2009 virus. The cumulative incidence of pandemic (H1N1) influenza was calculated as the difference between the point prevalence rates in the first and second panels. Results: Of the specimens collected in March, 7.1% were positive for the IgG antibodies (serum antibody titre ≥ 1:40). The corresponding prevalence was 15.7% among the specimens collected in August. The difference indicated a cumulative incidence of 8.6% (95% confidence interval [CI] 3.2%–13.7%). The rate differed geographically, the highest being in the northern regions (20.8%, 95% CI 7.9%–31.8%), as compared with 4.0% (95% CI 0.0%–11.9%) in Winnipeg and 8.9% (95% CI 0.0%–18.8%) in the rest of the province. Interpretation: We estimated that the cumulative incidence of pandemic (H1N1) influenza among pregnant women in Manitoba during the first wave of the 2009 pandemic was 8.6%. It was 20.8% in the northern regions of the province.